Since polymers having repeating units derived from a cycloolefin monomer are excellent in transparency, low hygroscopicity, heat resistance, insulation property, chemical resistance and the like, they have been broadly utilized as forming materials for optical members and the like such as optical lenses.
For example, Patent Literature 1 describes an addition copolymer of a norbornene-based monomer and ethylene. Further, this literature also discloses a copolymer of 1,4-methano-1,4,4a-9a-tetrahydrofluorene (MTF) and ethylene in Examples. This copolymer has a high glass transition temperature (Tg) and a high refractive index, and is useful as a resin component of an optical formed article.
In addition, the resin component of the optical formed article such as a lens requires excellent transparency. From this viewpoint, poly(methyl methacrylate), polycarbonate, diethylene glycol bisallyl carbonate, poly(cyclohexyl methacrylate), poly(4-methylpentene), amorphous alicyclic polyolefin, polycyclic norbornene polymer, a vinyl alicyclic hydrocarbon polymer and the like have conventionally been used as resin components of optical formed articles. For example, Patent Literature 2 describes an optical formed article obtained by using a forming material containing a polycyclic norbornene polymer having a specific repeating unit.
In recent years, lenses for mobile phone cameras and the like are required to be further thinner and to have enhanced resolution. Thus, a resin having not only excellent transparency but also high refractive index and low birefringence has been required.